1. Technical Field
The present invention relates to a test apparatus, an additional circuit, and a test board.
2. Related Art
When testing a device under test such as a semiconductor circuit, a power supply apparatus that supplies current to the device under test sometimes cannot quickly follow fluctuation in the current consumed by the device under test. A known technique for solving this problem, as shown in Patent Document 1, involves providing a bypass capacitor to the power supply line near the device under test.
Patent Document 1: Japanese Patent Application Publication No. 2001-195139
Patent Document 2: U.S. Pat. No. 6,087,843
A bypass capacitor is provided that has a large capacitance, e.g. tens of μF, capable of following a large fluctuation in the power supply current. In order to measure a low current, such as standby current, it is necessary to measure a low output current of the power supply apparatus. In this case, there is a limit on the load capacitance connected to the power supply apparatus, and so a lead relay is provided to disconnect a high-capacitance bypass capacitor from the power supply line.
However, since there are structural limitations near the device under test, a lead relay cannot be provided there. As a result, the high-capacitance bypass capacitor cannot be provided near the device under test, and is instead provided at a distance from the device under test.
Therefore, the power supply line from the bypass capacitor to the device under test is lengthened, which increases the inductance component between the bypass capacitor and the device under test. As a result, it becomes difficult to supply high-frequency current from the bypass capacitor to the device under test.
When the load current of the device under test fluctuates, the power supply voltage applied to the device under test temporarily drops due to the responsiveness of the power supply, the value of the bypass capacitor, and a voltage drop by the resistance component of the transmission path. Conventionally, the current supplied from the power supply or the high-capacitance bypass capacitor is measured, and so high-frequency components of the load current cannot be detected. Therefore, when the load current of the device under test fluctuates momentarily, the fluctuation of the load current cannot be detected, and so the acceptability of the device under test cannot be accurately judged.